1. Field of the Invention
The invention relates to a semiconductor laser comprising a semiconductor body having a substrate region of a first conductivity type and a layer structure disposed thereon which includes at least one first passive layer of the first conductivity type, a second passive layer of the second opposite conductivity type and an active layer interposed between the first and second passive layers. The active layer forms a pn junction which at a sufficiently high current strength in the forward direction can produce coherent electromagnetic radiation in a direction at right angles to that of the active layer in an active region of the active layer located within a resonant cavity situated between two reflectors. The layer structure also includes a current-limiting blocking layer of the second conductivity type, is interrupted at the area of the active region. The first and second passive layers and the blocking layer all have a larger band gap and a smaller refractive index for the radiation produced than the active layer, the first and second passive layers being electrically connected to connection conductors and the active region being laterally bounded by the blocking layer.
2. Description of the Related Art
Such a semiconductor laser is known from U.S. Pat. No. 4,309,670. This discloses a semiconductor laser in which an active layer having a homogeneous thickness produces radiation which emanates in a direction at right angles to the active layer. Current limitation is obtained by means of a buried blocking layer, which forms a reverse-biased pn junction with the adjoining semiconductor material. In one of the embodiments of this U.S. Patent, the active region is laterally bounded by an epitaxial semiconductor region having a larger band gap and a smaller refractive index for the emitted radiation than the active region.
Semiconductor lasers of the relevant type, in which the radiation produced is emitted in a direction at right angles to the active layer, have the advantage that they can be readily coupled to an optical fibre, the emanating beam is not very divergent and no accurate positioning of the crystal is required.
Since the length of the active region within which amplification occurs corresponds in known lasers to the thickness of the active layer and is consequently very small, a high current density is required to obtain the amplification required for the laser effect. In order to keep the threshold current at an acceptable value, fairly complicated epitaxial structures are required, while, as in the aforementioned U.S. Pat. No. 4,309,670, additional epitaxial passive layers and/or locally diffused blocking layers are used besides the active layer. For this reason inter alia, the said known laser structures can generally be realized only with great difficulty.